Highly efficient visible-light-driven g-C3N4/Ag3PO4 hybrid photocatalysts with different weight ratios of g-C3N4 were prepared by a facile in situ precipitation method and characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectrometry and UV-vis diffuse reflectance spectroscopy. Under visible-light irradiation (>440 nm), g-C3N4/Ag3PO4 photocatalysts displayed the higher photocatalytic activity than pure g-C3N4 and Ag3PO4 for the decolorization of methyl orange (MO). Among the hybrid photocatalysts, g-C3N4/Ag3PO4 with 25 wt % of g-C3N4 exhibited the highest photocatalytic activity for the decolorization of MO. The complete decolorization of MO was achieved for only 5 min of visible-light irradiation. X-ray photoelectron spectroscopy results revealed that metallic Ag particles on the surface of g-C3N4/Ag3PO4 hybrid were formed during the catalysts preparation. In addition, the quenching effects of different scavengers displayed that the reactive h(+) and O-2(center dot-) play the major role in the MO decolorization. The photocatalytic activity enhancement of g-C3N4/Ag3PO4 hybrid photocatalysts could be ascribed to the efficient separation of electron-hole pairs through a Z-scheme system composed of Ag3PO4, Ag and g-C3N4, in which Ag particles act as the charge separation center. The evidence of the Z-scheme photocatalytic mechanism of the hybrid photo catalysts could be obtained from a photoluminescence technique.